This invention relates to a blow-molded bottle-shaped container of biaxially oriented thermoplastic synthetic resin and a method of molding the same.
As the physical properties of a synthetic resin material and the molding technique of using the synthetic resin material have been advanced, a bottle-shaped container with a wide port closed by a caulked cap such as neocap made of aluminum is being molded by the synthetic resin material.
Since the bottle-shaped container with a wide port of this type is almost without exception used for containing drinking liquids and foodstuffs such as jams, filling of the drinking liquid in the bottle-shaped container is executed by heating filling and pressurizing filling.
Further, since the content liquid is filled by heating or pressurizing in the bottle-shaped container and the container is sealed, the container body itself must have sufficiently large mechanical strength. Thus, it is necessary to mold the bottle-shaped container with a wide port by a method of biaxially orientation blow-molding by the use of a polyethylene terephthalate resin.
A bottle-shaped container with a wide port which has sufficiently high mechanical strength can be provided by a method of biaxially orientation blow-molding the polyethylene terephthalate resin as described above. However, the blow-molded bottle-shaped container of biaxially oriented resin is biaxially orientation-molded only at the container body, but the neck edge portion to be associated with a caulked cap of the bottle-shaped container remains in the shape of the preformed primary injection-molded piece as the final shape as it is. Therefore, it is required to mold the preformed primary injection moded piece in high dimensional accuracy and so as to have sufficiently high mechanical rigidity.
In order to increase the mechanical rigidity of the neck edge portion, the thickness of the neck edge portion of the bottle-shaped container may be merely increased. However, it is very difficult to accurately hold the dimensional accuracy of the neck edge portion of the bottle-shaped container until the molding of the bottle-shaped container is completed.
More particularly, a conventional bottle-shaped container with a wide port of synthetic resin of this type has, as shown by hatched lines in FIG. 2, a structure that a container body 2 which is reduced in thickness is integrally formed by biaxial blow-molding directly from a thick neck edge portion 3. Therefore, it cannot accurately hold the dimensional accuracy of the surface of the neck edge portion 3 due to the variation in the radius (R.sub.1) of curvature of the lower surface 7 of the neck edge portion 3 and in the radius (R.sub.3) of curvature of the rear upper surface 9 owing to the flowing phenomenon from the body 2 side at the blow-molding time upon thermal influence of the heat to the body 2 at the biaxial-orientation blow-molding time of the preformed primary piece of the bottle-shaped container.
Further, when the body 2 which is biaxially orientation blow-molded in reduced thickness is integrated directly with the neck edge portion 3 as described above, the pressure and the heat acted on the body 2 affect to the neck edge portion 3 of the bottle-shaped container, thereby causing the size of the radius of curvature of the above-described surface part of the neck edge portion 3 to vary, with the result that the dimensional accuracy of the neck edge portion 3 becomes unstable.
The radius of curvature of the surface part of the neck edge portion 3 seriously affects the association of a cap 10 with the neck edge portion 3 for sealing the bottle-shaped container 1 with a wide port, and the radius (R.sub.1) of curvature of the lower surface 7 of the neck edge portion 3 is directly related to improved openability of the cap 10. Similarly, the upper surface, i.e., the radius (R.sub.2) of curvature of the front upper surface 8 and the radius (R.sub.3) of curvature of the rear upper surface 9 of the neck edge portion relate to improved sealability between the neck edge portion and the packing 11 of the cap 10. It is necessary to accurately hold the dimensions of the radii of curvature of the front and rear upper surfaces of the neck edge portion to the set value at the time of molding the preformed piece of primary injection-molded shape.
However, since the values of the radii of curvature of the front and rear upper surfaces of the neck edge portion in the conventional blow-molded bottle-shaped container with a wide port of biaxially oriented synthetic resin, cannot be held stable, opening of the cap 10 becomes difficult, the closing retentivity of the bottle-shaped container 1 by the cap 10, on the other hand, becomes insufficient, or the sealing effect of the packing 11 associated with the cap 10 is not sufficient, with the result that the quality of the content liquid in the bottle-shaped container is disadvantageously deteriorated, or varied.